To start using the new feature, tap Photos>More>Settings>SkyDrive. Here’s what it looks like visually:

Now, instead of the menu on the left, you’ll now see the one on the right. Just tap Best quality to upload your photos or videos in the highest resolution. One caveat: To save your phone bill, it does require a Wi-Fi connection. (Learn more about the feature.)

Remember, the update was just rolled out so you might not notice a difference for a few days.